Periodontal disease is characterized as local inflammatory response with associated soft tissue damage and bone loss. The bone loss is due to a complex set of interactions, which are poorly understood, between activating agents, immune cells, and bone cells. Bacteria and their products appear to be the major activating agents of this response. Immune cells and their cytokines mediate both the local response and the subsequent systemic response. These cytokines are regulatory not only for immune cells, but they also have a profound effect on bone cells and particularly osteoblasts. This point is of added significance since bone cells secrete many of these same cytokines. Osteoblasts also express cell surface activating determinants similar to those found on T cells.Thus, osteoblasts appear to play a central role as regulators of normal bone homeostasis as well as during pathological stimulation. However, little data is available on the mechanisms leading to osteoblast activation and the autocrine and paracrine regulatory interaction mediated by the secretion of bone cell derived cytokines. These cytokines may regulate not only bone cell activity but also hematopoietic and immune cell function. Therefore, the long term goal of this proposal is to study the mechanisms of osteoblast activation utilizing functional, serological, biochemical, and molecular techniques to assess that activation and concomitant cytokine release. Three apparently distinct methods of osteoblast activation will be examined. This study will 1) determine the regulatory circuitry of cytokine secretion by osteoblast activation with lipopolysaccharide; 2) Determine the role interleukin 6 plays in osteoblast activation; and 3) Identify and determine the role the cell surface determinants Thy-1 and Ly-6 plays in osteoblast activation and identification of subsets. Primary murine osteoblasts and the cloned osteoblast line MC3T3 will be activated in vitro by osteotropic agents (LPS, PTH, retinoic acid, etc.) or antibodies directed at specific cell surface determinants. Functional, serological and biochemical experiments will be used to determine the profile of cytokines secreted and their interactions with other cells. Monitoring osteoblast mRNA will be used to determine changes at the molecular level. Immunohistochemical experiments will be used localize specific cell surface activating determinants to osteoblasts and trace osteoblast development. A better understanding of how osteoblasts are activated, the cell interactions involved and the resulting cytokine release will certainly lead to a clearer understanding of the pathogenesis of both periodontal disease and other lesions associated with bone remodeling. This information can then be used to develop more rational therapies to treat these diseases.